A wide variety of strategies has been used to enhance the productivity of food crops, including the use of fertilizers as nutritional supplements, application of pesticides to counteract the negative effect of infestation, and supplementation with growth hormones such as auxins and gibberellic acids. Each of these approaches, especially when implemented using synthetic materials, poses problems with respect to unacceptable alteration of the environment and concomitant unbalancing of the ecosystem.
It is understood that plant growth regulators are produced by some fungi. For example, gibberellins, indole-acetic acid, cytokinins, and other compounds useful in regulating plant growth are found in Basidiomycetes as reviewed by Brizuela, M. A., et al., Revista Ibero Americana de Mycologgia (1998) 15:69-74; the plant growth regulator dihydroampullicin is produced by a fungus Ampulliferina (Kimura, Y., et al., Bioscience Biotech. & Biochem. (1993) 57:687-688) and it is generally known that Neurospora and various phytopathogenic fungi produce plant growth regulators. It is also known that Polyporus versicolor, a white rot polypore produces plant growth regulators. However, culture conditions to enhance the production of plant growth factors vary widely.
Basidiomycetes have been shown to produce gibberellins, auxins, indoleacetic acid, abscisic acid, cytokinins and ethylene, as well as other plant stimulatory metabolites. The production of these factors, however, has been shown in the context either of production when in association with a plant per se, or on small-scale laboratory bases.
The present invention provides a method to provide plant growth factors from fungi, in particular Basidiomycetes, on a commercial scale. It has been generally considered not possible to do this. For example, according to “Handbook of Applied Mycology,” Vol. 4, Fungal Biotechnology (1992) page 588                It is interesting to note that the species of Taphrina and Exobasidium formed yeasty like cells and spores in surface layers on the parasitized tissues of the host plant. When grown on submerged fermentation (SMF) process in synthetic media, the cytokinin (CK) production by these fungi was too small to cause extensive morphological changes that occur naturally in the host plant in spite of the growth in SMF medium in the form of yeast like cells. It was therefore stressed that the production of CK by pathogenic hyphal cells of Taphrina growing on host tissues was undoubtedly different in quantities. The close resemblance of the growth of the fungi under solid state fermentation technique to the above type of growth of the fungi on the host tissue is well known.        
Further, according to this source,                It is obvious that the obligate parasitic, mycorrhizal, ascomycetous, and basidiomyceteous fungi have no potential in fermentative production of CK (cytokinin) due to problems in cultivation and slow growth rate.        Downstream processing involves handling of large volumes of liquid for separating extremely low quantities of GA3 (Gibberellic Acid 3), and thus is cost intensive when compared to other fermentation products such as citric or gluconic acids.        After separation of mycelial cells by filtration or centrifugation, GA3 is either adsorbed on suitable resins/adsorbents or extracted in appropriate solvents. Further purification involves a series of operations such as repeated liquid-liquid partitioning, concentration under vacuum, and final processing to obtain amorphorus powder or crystals of GA3.        
Thus, even if it is known that certain plant parasitic fungi may produce plant growth regulators, the fungi may not produce the plant growth regulators (PGR) in quantity in fermentation systems to be of practical use unless culturing, extraction and concentration steps are taken.
It has now been found that an environmentally friendly stimulant of growth can be supplied by composting agricultural waste in the presence of fungal spawn, sterilizing the culture filtrate, and applying the resulting “liquid compost factor (LCF)” directly to field crops even after diluting with water 1 to 500 or up to 1:10,000. There is no need for extraction or chemical separation steps in order to obtain a useable solution. Only heating and filtration are needed. No solvents or resin beds are needed for extraction or concentration. The solids and filter material itself from filtration step of the heated liquid culture fluid may be dried and used as a source of plant growth stimulants as well. The dried material may be added to compost as an additive.